1. Field of the Invention
This invention relates to a device for transmitting signals from a fixed body to a rotary body, or from a rotary body to a fixed body, through a rotary mechanism. More specifically, this invention relates to a rotary light coupler which is capable of transmitting the signals without contact with the object to which the signals are to be transmitted, through a rotary mechanism, using an optical communication device to improve the reliability of the transmission.
2. Description of the Prior Art
In an apparatus having a rotary part such as an arm of a robot, a rotary head of an electronic parts mounting apparatus or a functional part of a game machine, an actuator (an electric motor in most cases) and its control device are usually mounted in the rotary part. In such cases, it is necessary to supply power from a fixed body that is the main body of the apparatus, into a rotary body that is the rotary part of the apparatus. It is also necessary to transmit control signals from the fixed body to the rotary body, or from the rotary body to the fixed body in a certain case. Such supplying of power and transmitting and receiving of signals are required to be made through a rotary mechanism. A brush and slip ring that contact with each other (contact type device) have been used in general for supplying power or transmitting and receiving signals.
In a contact type device in which a brush and a slip ring are used for supplying power or for transmitting and receiving signals, through a rotary mechanism, problems often occur with regard to the quality of the signal transmission and receiving and with regard to the durability of the devices. Further, in case that a large number of actuators or control devices are mounted on a rotary body, and that their respective control signals are transmitted in parallel, the number of slip rings increases. As a result, the signal transmission and receiving device becomes bulky, complicated and expensive. These control signals may be transformed into serial signals to be transmitted in a serial communication through a slip ring, or a pair of slip rings disposed in parallel for higher reliability of transmission. In such a serial communication, however, the communication becomes more susceptible to noises generated at the slip ring or slip rings, particularly when the communication speed becomes higher. In general, the noises increase with the amount of time the slip ring is used. Accordingly, life span of the slip ring with regard to noise emission as well as wear by friction is a matter to be fully considered. Since power supply devices are less susceptible to noises comparing with signal transmission and receiving devices, brushes and slip rings may still be used in the power supply devices in various fields. Accordingly, it is desired to realize signal transmission through a rotary mechanism with a non-contact type transmission and receiving device without using a brush and a slip ring. In any case, contact type transmission and. receiving devices will become useless sooner or later, since the rotation speed is going to be faster and the wearing of the devices will become a fatal problem. It will also become necessary to make power supply devices non-contact type.
A non-contact type power supply device and signal transmission and receiving device are disclosed, for example, in a publication, Japanese Unexamined Patent Publication (Kokai) No. 8-97597, xe2x80x9cAN ELECTRONIC PARTS MOUNTING APPARATUSxe2x80x9d. In the publication, a non-contact type power supply device comprising a rotary transformer utilizing DCxe2x80x94DC converter and a non-contact type signal transmission device comprising a rotary transformer utilizing high frequency modulation are disclosed. Further, it is mentioned in the publication that the non-contact type signal transmission device can be replaced by an optical communication device, however, no embodiment for the optical communication device is disclosed.
A non-contact type signal transmission device utilizing a rotary transformer, such as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 8-97597, is being used generally in a rotary head of a VTR set. Signal transmission performance of a rotary transformer is influenced greatly by a gap of the transformer. That is, it is necessary to make the gap of the transformer as narrow as possible to obtain the rotary transformer of an excellent performance. If the rotary transformer is an axial-gap type transformer, then axial run out of an end surface of a core of the transformer is required to be suppressed within a minimum value. If the rotary transformer is a radial-gap type transformer, then radial run out of a core of the transformer is required to be suppressed within a minimum value. As a result, high accuracy is required for manufacturing and assembling such rotary transformers, which makes these rotary transformers very expensive.
A rotary transformer may be adopted as a power supply device in place of brushes and slip rings to make a power supply device non-contact type. In this case, leakage of magnetic flux increases with the increase of power to be transmitted. Accordingly, a rotary transformer for signal transmission and receiving device disposed close to the rotary transformer for power supply device need to be shielded from the magnetic flux, which also makes the signal transmission device expensive. In these cases, a signal transmission and receiving device utilizing an optical communication device is more preferable, since an optical communication device is less susceptible to the magnetic field caused by the power supply device.
Conventional optical communication device that can be used as a bi-directional (transmission and receiving) communication device in a rotary mechanism has, in general, a complicated optical system comprising lenses, mirrors and/or prisms.
It is an object of the present invention to provide a rotary light coupler for a signal transmission and receiving, utilizing an optical communication device, through a rotary mechanism.
It is a more specific object of the present invention to provide a rotary light coupler, having very simple structure without using complicated and expensive optical system, for a bi-directional non-contact type signal transmission and receiving device.
In order to accomplish the above objects, the present invention provides a rotary light coupler comprising a first light emitter and a first light receiver mounted on a fixed body, and a second light emitter and a second light receiver mounted on a rotary body, in which the first light emitter is arranged to transmit light beam containing signals to the second light receiver through a rotary mechanism, the second light emitter is arranged to transmit light beam containing signals to the first light receiver through the rotary mechanism, the first light receiver and the second light receiver are placed opposing each other along the direction of the axis of rotation of the rotary body, the first light emitter and the second light emitter are placed respectively at the radially outside of the first light receiver and the second light receiver, a light axis of the first light emitter is set in such a manner that it is directed toward the central portion of the second light receiver and that a reflected light from the second light receiver does not enter into the first light receiver, a light axis of the second light emitter is set in such a manner that it is directed toward the central portion of the first light receiver and that a reflected light from the first light receiver does not enter into the second light receiver, and a set of the first light receiver and the first light emitter and a set of the second light receiver and the second light emitter are disposed in such a manner that they do not mechanically interfere with each other when they rotate relatively with each other.
Preferably, a light emitter with a narrow light spread angle is used for the first or the second light emitters, so that the light beam transmitted by the first light emitter does not come into the first light receiver, and that the light beam transmitted by the second light emitter does not come into the second light receiver.
If necessary, side surfaces of the first light emitter and the second light emitter are covered with covers formed of a light shielding material, to narrow down the light beams emitting from the first light emitter and the second light emitter to make the light beams direct only to their respective directions to which the light beams are to be directed.
Further if necessary, the first light emitter and the first light receiver are placed in a first case defining positions and orientations of the first light emitter and the first light receiver, and the second light emitter and the second light receiver are placed in a second case defining positions and orientations of the second light emitter and the second light receiver, then the first case and the second case are placed to oppose each other.
Preferably, the first case and the second case are formed of a light shielding material to suppress unnecessary lights emitting from the first light emitter and the second light emitter, and to suppress unnecessary lights entering into the first light receiver and the second light receiver.
A rotary power supply apparatus with rotary light coupler for signal transmission and receiving can be obtained by attaching the rotary light coupler in accordance with the present invention to an end portion of a shaft on which slip rings for power supply are provided.
Another rotary power supply apparatus with rotary light coupler for signal transmission and receiving can be obtained by attaching the rotary light coupler in accordance with the present invention to an end portion of a shaft on which a rotary transformer for non-contact power supply is provided.
According to the present invention, the set of the first light receiver and the first light emitter and the set of the second light receiver and the second light emitter can rotate relatively without mechanically interfering with each other. The light axes of the light emitters are directed toward the central portions of the respective light receivers to which the light beams are to be directed, and these light beams can be transmitted to the respective light receivers even when the light beams cross each other. Thus, a non-contact type bi-directional transmission can be performed using an optical system of very simple structure, without using a complicated optical system comprising lenses, mirrors, prisms and/or the like.
Further according to the present invention, S/N ratio of signal transmission can be improved by covering side surfaces of the first light emitter and the second light emitter with covers formed of a light shielding material, to narrow down the light beams emitting from the first light emitter and the second light emitter to make the light beams direct only to their respective directions to which the light beams are to be directed.
Positioning of the light emitters and the light receivers, and setting of light axes of the light emitters, can be made easily by placing the light emitters and the light receivers in the cases defining positions and orientations of the light emitters and the light receivers.
S/N ratio of signal transmission can further be improved by forming the cases with light shielding material to suppress unnecessary lights emitting from the light emitters and entering into the light receivers.
Power supply and signal transmitting and receiving, through a rotary mechanism, of high reliability can be realized by attaching the rotary light coupler of the present invention to an end portion of a shaft on which slip rings for power supply are provided, in which power supply is made by a contact type device comprising slip rings and brushes, whereas signal transmission and receiving are made by non-contact type rotary light coupler.
Further, power supply and signal transmission and receiving, through a rotary mechanism, of high reliability can be realized by attaching the rotary light coupler of the present invention to an end portion of a shaft on which a rotary transformer for power supply is provided, in which power supply and signal transmission and receiving can be made by non-contact type devices.